Caffeine calculator: how much is left at bedtime?
Caffeine has a half-life of roughly 5-6 hours. Enter your intake and target bedtime to see how much will still be active, and when to stop.
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Why caffeine timing matters for sleep
Caffeine blocks adenosine, the molecule that builds up sleep pressure during the day. Even if you fall asleep fine, residual caffeine in your system can reduce deep sleep and increase night-time awakenings — often without you noticing why you slept poorly.
Frequently asked questions
How long does caffeine really stay in your system?
Its half-life is about 5-6 hours on average, though this varies by person — meaning roughly half the caffeine is still active that many hours later.
Does this apply to tea and energy drinks too?
Yes — this calculator works for any caffeine source; just enter the approximate milligram amount for what you consumed.
Want to go further?
Explore our guides and other calculators.